linux-kernel - [PATCH] kfence: Replace local_clock() with ktime_get_boot_fast

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Message-ID: <VI1P193MB0752A2F21C050D701945B62799BAA@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM>
Date:   Wed, 22 Nov 2023 20:00:26 +0000
From:   Juntong Deng <juntong.deng@...look.com>
To:     glider@...gle.com, elver@...gle.com, dvyukov@...gle.com,
        akpm@...ux-foundation.org
Cc:     kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: [PATCH] kfence: Replace local_clock() with ktime_get_boot_fast_ns()

The time obtained by local_clock() is the local CPU time, which may
drift between CPUs and is not suitable for comparison across CPUs.

It is possible for allocation and free to occur on different CPUs,
and using local_clock() to record timestamps may cause confusion.

ktime_get_boot_fast_ns() is based on clock sources and can be used
reliably and accurately for comparison across CPUs.

Signed-off-by: Juntong Deng <juntong.deng@...look.com>
---
 mm/kfence/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 3872528d0963..041c03394193 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -295,7 +295,7 @@ metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state nex
 	track->num_stack_entries = num_stack_entries;
 	track->pid = task_pid_nr(current);
 	track->cpu = raw_smp_processor_id();
-	track->ts_nsec = local_clock(); /* Same source as printk timestamps. */
+	track->ts_nsec = ktime_get_boot_fast_ns();
 
 	/*
 	 * Pairs with READ_ONCE() in
-- 
2.39.2